A "cone" or "flame" shaped diamond Dremel bit should work. Here is an example link, contains multiple shapes: [24Pcs Diamond Grinding Bits Set, 3mm Shank Diamond Mounted Point Rotary Burrs, Grinding Drill Carving Rotary Tool for Glass Stone Ceramic Carving Polishing (4 shaped) https://www.amazon.com/dp/B09D86V28Z/ref=cm_sw_r_cp_api_glt_i_YPCWVKTHSK515K1PRKSH](link)